The Foraminiferal Signature of Hurricanes: Mississippi Delta, Shelf, and Canyon, Northern Gulf of Mexico, USA

Hurricane Ivan (2004) and Hurricanes Katrina and Rita (2005) caused extensive sediment resuspension and redistribution on the northern Gulf of Mexico shelf. This study investigates the utility of foraminifera in identifying storm units on the continental margin, in an area stretching from the Southwest Pass of the Mississippi Delta to the upper reaches of the Mississippi Canyon. Five box cores and one kasten core were used for analysis. Two cores were collected after Hurricane Ivan and four after Hurricanes Katrina and Rita.

Foraminiferal assemblages proved to have distinct patterns in storm versus non-storm units. In 80 m of water, a mid-shelf core (between the delta and canyon) contains sedimentary units deposited during Katrina and Rita which show increased total numbers of foraminifera per unit volume near the top of each unit. Despite an increase in the total number of foraminiferal tests, the percent of agglutinated foraminifera decreases almost to zero. Agglutinated foraminiferal percentages are greater in the Katrina than in the Rita unit; the trend is the same for the percent of broken foraminiferal tests. Percentages of planktonic foraminifera are lower in the pre-hurricane unit than in hurricane-deposited units; however, in a Mississippi Canyon core (water depth 508 m) the opposite trend is observed.

Foraminiferal species also show different patterns in storm versus non-storm units. In the mid-shelf core, Epistominella vitrea, Buliminella bassendorfensis, and Nonionella opima are observed in non-storm units, whereas in storm units at the same depth, Textularia earlandi dominates with a reduction in total numbers per unit volume of Epistominella vitrea, Buliminella bassendorfensis, and Nonionella opima.

Based on these preliminary results, storm units can be distinguished from non-storm units, thus demonstrating transport of foraminiferal tests during these high energy events. Furthermore, foraminiferal signatures vary depending on the water depth and location on the continental shelf/upper slope.